I can't help you myself, but here is a web site that will lead you to others on math: go to www.lynnreedy.com, click on grade-level resources, click on K-5, and scroll until the end. Many of the sites are the same, but go to the 5th grade ones just to be sure. If you can't find sites there that explain, hit the "back" key until you're back to the K-5 page and click on 6-12. The web sites are arranged topically. There are a lot for math! Good luck!